The invention relates to a cylinder/piston aggregate rotating together with a shaft which is concentrically arranged with respect to the aggregate.
The cylinder/piston aggregate is designed for a medium of varying pressure, and either the piston or the bottom of the cylinder is in rigid connection with the shaft. The element not connected to the shaft undergoes a movement in circumferential and/or in axial direction relative to the element connected to the shaft. A seal is provided between the piston and the inner cylinder wall.
Aggregates of this type are, for example, employed in infinitely variable cone pulley transmissions, but the scope of the invention is not limited to this kind of use. In such transmissions the cylinder/piston aggregate is connected to the cone pulley of the pulley pair on one shaft which is displaceable on the shaft in an axial direction. By means of the aggregate the pressure is generated which the pulleys exert on the transmitting belt. This pressure may also be generated purely mechanically by cam elements. In this case the hydraulically generated pressure supports the mechanical pressure. The cam elements are usually arranged within the cylinder and comprise a cam on the axially displaceable cone pulley, a cam on a ring mounted rigidly on the shaft, and roller members inserted between the cams. The cam ring is usually so designed as to constitute at the same time the piston of the cylinder/piston arrangement.
Now, the pressure exerted by the cone pulleys of one transmission side on the transmitting belt plus the pull exerted by the belt on the cone pulleys and on the shaft cause the shaft to be slightly bent in the direction of the other transmission shaft. The shaft deflection in this particular direction prevails throughout all operations of the transmission, i.e. whenever the shaft rotates.
This causes the sealed-off gap between the piston and the cylinder wall to be continuously narrowed and widened in a circumferential direction. Consequently every portion of the seal between the piston and the cylinder wall is alternately pressed together and relieved from pressure with the frequency of the shaft rotation. This effect may be termed the "squeezing effect" and causes the seal to become hot and to get worn, especially at the surfaces in the axial direction, but also at its outer and inner surface because the seal also moves in a circumferential direction on account of the fulling effect. The wear of the seal is particularly heavy if the number of shaft rotations is high and the pressure of the medium to be sealed off is also high. The wear is then so heavy that the sealing ring breaks at the place of the smallest cross section.
The described deflection of the rotating shaft imposes a wear on the seal which differs essentially from the strains to which the transmission seals are normally exposed. These normal strains are brought about by sliding movements in the axial and circumferential directions and the seals are adjusted thereto by a particular shape and design. This different wear caused by the squeezing effect is also indicated by the fact that mainly those portions of the seal are worn which do not directly bring about the sealing effect, i.e. the main body of the sealing ring, which is relatively unelastic compared with the sealing edges of the ring. These conditions prevail with all seals normally known and suitable for this purpose, i.e. seals which do not have too much residual stress, so that the transmission may easily be adjusted to various transmission ratios.
It is, therefore, the object of the present invention to provide a cylinder/piston aggregate which overcomes the above difficulties, and it is a further object to overcome these difficulties without employing other than the usual sealing means between the piston and the inner cylinder wall.